Many illumination designs benefit from homogenized light. Accordingly, efforts have been made to obtain substantially uniform illumination distributions from light sources, such as light emitting diodes (LEDs) that produce non-uniform illumination distributions. One known method of achieving this goal employs mixing rods. In many embodiments, flux from a light source is transferred to an input end of a mixing rod. The flux propagates through the mixing rod, typically reflecting from the sidewalls of the mixing rod one or more times. In certain embodiments, coupling a light source that produces a non-uniform illumination distribution with the input end of the mixing rod produces a substantially uniform illumination distribution at an output end of the mixing rod.
Certain mixing rod configurations are particularly effective in achieving substantially uniform illumination distributions. For example, straight rods having rectangular or hexagonal cross-sections are known to work well. Such configurations produce rectangular and hexagonal beam patterns, respectively. However, circular beam patterns are preferred in many applications, such as flashlights, spotlights, fiber illuminators, and projection systems with circular pupils. Unfortunately, circular straight rods generally provide inferior spatial mixing as compared with rectangular or other faceted configurations. Accordingly, hexagonal mixing rods are often used in place of circular mixing rods in order to approximate a circular beam pattern while achieving the advantages of a mixing rod having planar sidewalls.
It is known to combine mixing rods with a zoom lens for changing the divergence of the light beam. However this results often in the fact the an illumination distribution not substantially uniform illumination distributions in the entire zoom range, as the known mixing rods are designed such that they only provide a uniform/homogenized in a certain plane of long the light beam for instance at an optical gate. Consequently, there is a need for mixing rods that produce circular beam patterns that have substantially uniform illumination distributions. Further there is a need for mixing rods which can be combined with a zoom lens and maintain a substantially uniform illumination distribution in the entire zoom range.
U.S. Pat. No. 6,219,480 discloses an optical coupler for coupling light along an axis between a light port on one side of the coupler and a plurality of light ports on another side of the coupler. The coupler comprises a one-side stage with a light port and a many-side stage with a plurality of arms situated about the axis, each having a light port. A midput region separates the one-side and many-side stages and is situated along the axis where the plurality of arms at least initially starts to split from each other in a direction towards the many-side light ports along the axis. Cross sections of each of the respective initial portions of the arms along the direction are arranged about the same distance from the axis. The cross sectional areas of the arms along the axis are larger at a break point region at which the arms fully separate from each other along the axis than at the many-side light ports. At least a pair of the arms each start to split along the direction in a substantially symmetrical manner about the axis.
US2007/0024971 discloses various embodiments of light mixers comprising a light pipe having input and output ends and a central region there between. An optical path extends in a longitudinal direction from the input end through the central region to the output end. The central region of the light pipe comprises one or more rippled reflective sidewalls having a plurality of elongate ridges and valleys and sloping surfaces there between. Light from the input end propagating along the optical path reflects from the sloping surfaces and is redirected at a different azimuthally direction toward the output end thereby mixing the light at the output end. In some embodiments the cross-sectional shape and area of the mixer are constant along the full length of the mixer and the input face and the output face are the same shape and size. In other arrangements, the cross-sectional shape and/or area of the mixer vary along the length thereof and the input face and the output face may vary with respect to each other in shape and/or size. In some instances, the input face defines a rectangle or square and the output face defines a circle or vice versa. US2007/0024971 explicitly teaches that it is the rippled relective sidewalls and not the shape of light mixer that improves the homogenisity of the outgoing light beam. However the rippled reflective sidewalls of the light mixers are difficult to manufacture as they must be designed with very low tolerances which increases the manufacturing costs dramatically. Further the light mixers having the rippled relective sidewalls need to be positioned very accurate in relation to the light sources, which again increases manufacturing costs.
U.S. Pat. No. 6,200,002 discloses a light source which includes an array of LEDs in each of a plurality colors such as red, green, and blue in the entrance aperture of a tubular reflector which preferably has convex walls facing the optic axis and flares outward toward the exit aperture, and preferably has a polygonal cross section such as a square. Mixing of colors is further promoted by utilizing a large number of small LEDs with the LEDs of each color being centered on the optic axis.
U.S. Pat. No. 6,547,416 discloses A light source, which includes an array of LED components in each of a plurality of colors such as red, green, and blue in the entrance aperture of a tubular reflector which has an exit aperture, an optic axis extending between the apertures, and a reflective circumferential wall extending between the apertures to reflect and mix light from the array of LED components. At least a portion of the circumferential wall of the reflector body has a polygonal cross-section taken normal to the optic axis, and at least a portion of the cross-section taken parallel to the optic axis includes segments of a curve joined one to the next to form a plurality of facets for reflecting light from the LED components to said exit aperture. Preferably, the segments of the curve included in the cross-section of the reflector body taken parallel to the optic axis are contiguous, linear trapezoidal facets.
EP2211089 discloses an apparatus for outputting a mixed-colored light beam comprises a light mixer and a lens. The light mixer is adapted to mix light received from at least two light emitters, each of the two light emitters having a differently colored light output, wherein the mixer is adapted to mix the received light so that a mixing degree of mixed light output by the mixer is at least 50 percent, wherein a mixing degree of 100 percent is a fully mixed light. The lens is spaced apart from the light mixer, wherein the lens is attached to a lens holder in such a way that the lens can be moved with respect to the light mixer in order to vary a size of the mixed-colored light beam output by the lens. EP2211090 discloses a spotlight comprising light emitting diode modules wherein each LED module comprises at least two light emitting diodes with different light emission spectra and a light mixer, wherein each light mixer is arranged at one side of the light mixer in cooperation with an assigned LED module and each light mixer is configured to mix the different light emission spectra of the at least two LEDs of the assigned LED module to form a light beam, and wherein exit surfaces at the other side of the light mixers are arranged next to each other in a matrix with its light beams of the light mixers form a common light beam and a focusing optics for focusing the common light beam. EP2211089 and EP2211090 disclose that an iris can be positioned in the common light beam in order to create a circular light beam by chopping the common light beam. However this will decrease the efficiency and efficacy of the light system.
WO10113100A discloses an LED collimation optics module and luminaire using the same, and optics device for stage lighting. In one embodiment of the LED collimation optics module, an LED chip provides a plurality of sources of light (G, R, B, W). An optical conductor is superposed on the LED chip to mix the light received from the plurality of sources of light. After passing through the optical conductor, the mixed light enters a compound parabolic concentrator which is coupled to the optical conductor. The compound parabolic concentrator collimates the light received from the optical conductor such that a homogeneous pupil is emitted. This light mixing optics are relativily long and an illumination device which this type of light mixing optics are thus also to very long which is undesired in connection with moving head light fixtures as it can decrease the speed of movement of the moving head. It is further difficult to integrate the LED collimation optic modules into a zoom effect system in an effective way as such zoom effect system must be very large in order.